1. Field of the Invention
The present invention generally relates to semiconductor integrated circuits, and more particularly, the present invention relates to temperature sensing circuits.
2. Description of the Related Art
FIG. 1 is a circuit diagram of a conventional temperature sensing circuit. As illustrated in FIG. 1, the conventional temperature sensing circuit includes a first current source 10 and a first diode 12 connected in series between a source voltage VDD and a ground voltage, and a second current source 14 and a second diode 16 connected in series between the source voltage VDD and the ground voltage. Each of the current sources 10 and 14 outputs a constant current Iref. Further, an area NJ of the second diode 16 is N times larger than an area J of the first diode 12, where N is an emitter current density ratio (e.g., between the first and second diodes 12 and 16). A voltage delta ΔVBE is utilized to measure temperature, and in an ideal case, ΔVBE may be calculated using the following equations:VBE1=VT(ln(NIref/IS))  [Equation 1]VBE2=VT(ln(Iref/IS))  [Equation 2]ΔVBE=VT(ln(N))  [Equation 3]VT=kT/q  [Equation 4]
In the above equations, VT denotes thermal voltage, k is Boltzmann's constant, q denotes electron charge (constant), T denotes (absolute) temperature, IS denotes a saturation current (constant in a corresponding device) and N is an emitter current density ratio.
As illustrated in the graph of FIG. 2, in an ideal case, ΔVBE is proportional to absolute temperature (PTAT). However, ΔVBE actually has non-ideal effects that cause error in reading a temperature. In a non-ideal case, ΔVBE is represented as follows:VBE1=VT(ln(NIref+α/IS))+(NIref+α)R  [Equation 5]VBE2=VT(ln((Iref+β)/IS))+(Iref+β)R  [Equation 6]ΔVBE=VT(ln((NIref+α)/(Iref+β)))  [Equation 7]
Here, α and β represent current gains, which are dependent on temperature variations.
Non-ideal components, such as α and β, cause non-linear characteristics, which make it difficult to accurately sense temperature. This causes conventional temperature sensing circuits to produce erroneous temperature data.